In combat situations, or in situations in which troops and vehicles are deployed for policing purposes, combat vehicles and personnel are subject to attack at very close range through the use of rocket-propelled grenades (RPGs) or other ordinances which are launched from sites which are very close to the personnel or vehicles. Thus, troops and vehicles are subject to weapons launched in their immediate vicinity. There is therefore a need to be able to detect an incoming missile and to countermeasure it all within the space of, for instance, less than a second.
This presents challenges not only to the countermeasure system in which one might, for instance, have to aim and fire a so-called shotgun in the direction of the incoming missile with a sufficiently dense pellet pattern but also to be able to detect and track where the incoming missile is in the first place.
For instance, personnel and vehicles are oftentimes attacked from very close range in tens of feet, where enemy personnel launch a missile, for instance, from the side of a road or from a nearby building.
While one could attempt to detect the launching of such a missile using radar, the use of radar to provide situational awareness in the immediate proximity of a vehicle suffers from a number of problems.
Since the reaction time is a fraction of a second to a second, not only would the response time need to include being aware of some kind of munition, one would also have to include the amount of time necessary to countermeasure the threat.
In order to countermeasure such close-in threats, one would have to localize the projectile to its own size. Thus, if the missile is, for instance, a foot long and six inches in diameter, one would have to know where the missile was to the same accuracy so that one effectuates a direct hit.
As will be appreciated, microwave radars might not have sufficient resolution to be able to pinpoint the incoming missile. Moreover, such radars generally have rotating heads that move an antenna around to cover a specific area. There is thus an associated scan time that may be much too long to permit effective countermeasuring of an incoming missile.
There is also an associated processing time when using a radar involving calculating the trajectory of the missile and what is necessary to countermeasure it. Thus, there is a calculational lag that may put the response time outside of the fraction of a second response time required.
By way of further background, optical rangefinders are well known in gunnery to determine the distance to a target. In a basic form, such devices may be constructed to give the solution of a triangle having the target at its apex and the rangefinder at the lower base.
The prior art discusses improvements on optical rangefinder designs. U.S. Pat. No. 4,062,267 to Vinches et al., for example, discloses apparatus for conducting firing adapted to the aiming of a cannon movable bearing and in elevation around a turning axis as a function of aim values given by a firing table. The apparatus comprises a telescopic sight with an optical deviator element for displacement of the line of sight, the optical deviator element being mounted on a support coupled in bearing and in elevation with the cannon and being subjected to the action of a cam whose profile is determined by the aim values from the firing table and which is coupled to a motor controlled by a rangefinder device whose transmission and reception beams are connected in bearing and in elevation to the axis of the observation scope of the telescope. The optical deviator element is articulated through the intermediary of a spherical articulation on the support connected to the cannon and the optical deviator element is subjected to the signal of a detector of the vertical operating so that the observation axis must be maintained in a substantially vertical plane passing through the direction of the target.
While such devices have tended to work well for the purpose of controlling fire directed against stationary or slow moving targets at a substantial range, these devices have limitations with respect to fast moving targets in close proximity to the sensing vehicle or structure.
U.S. Pat. No. 4,556,313 to Miller et al. discloses a rangefinder that is adapted for use as a proximity fuse. This patent discloses an optical rangefinder having a transmitter and receiver located closely adjacent for short-range operation, as when a projectile or bomb is sent on a trajectory to intercept a large object. An optical window region is established where the transmitter look axis intersects the receiver look axis and is adjustable for providing an output signal when the rangefinder and target are less than approximately ten feet apart. The transmitter may emit either noncoherent or coherent infrared energy. The receiver includes zero crossing detection when a received maximum signal intensity is reached and adequate signal detection means that activates when the signal level exceeds a desired minimum. An output signal is generated when the outputs of these two detection circuits are coincident.
This system, however, does not address the problem of detecting incoming projectiles or missiles that can be coming in from all directions. Also it does not address the issue of computation time that is exceedingly short when it is necessary to detect and localize close-in missiles or projectiles.
A need therefore exists for a close-in system that does not involve location calculations or slewing of optics. In particular, a need exists for a for a system that may be used to accurately determine the existence and range of an approaching rocket-propelled grenade, RPG, or other rapidly-moving ordnance.
While the prior devices have tended to work well for the purpose of controlling fire directed against stationary or slow moving targets at a substantial range, these devices may have limitations with respect to fast moving targets in close proximity to protected vehicles or personnel.